Gas turbines in general, and perhaps aircraft engines in particular, are exposed to many kinds of fouling during operation. The fouling is caused by material that is sucked into the turbine via its air inlet. The material can be of many kinds such as particles from exhaust gases, insects, larger animals such as birds, atmospheric pollution such as soot, etc. All these materials adhere to turbine blades and form fouling coatings that adversely affects the operation of the turbine, by decreasing the air flow of the turbine's compressor, thereby decreasing the overall performance of the gas turbine.
Compressor cleanliness can be maintained using a routine program of water washing. Two such water wash maneuvers performed on gas turbines are referred to as off-line and on-line, respectively. An off-line maneuver is conducted with the gas turbine in a cooled state using cranking speed, while an on-line maneuver is conducted with the gas turbine at operating temperature. This on-line maneuver typically uses water only. Both washing maneuvers use highly atomized water spray patterns designed to completely enter a turbine's compressor core. The off-line cleans the entire core and recovers lost performance, while the on-line cleans the early stages of the core and maximizes the time period between needed off-line washings.
Known systems for washing turbines are directed to cleaning engine turbines on aircrafts, or stationary industrial turbines. Cleaning APUs, however, which are provided for generating electricity to aircrafts during stops at airports, has not been addressed by the known systems.
Instead, it is common practice to dismantle an APU from the aircraft and either replace it, or to clean it separately and re-mount it into place.
As can be appreciated by those in the art, such a procedure is fairly tedious, and as a result, there is a tendency to allow large time intervals lapse between cleaning/replacement of APU's. As a consequence, an APU can lose some of its power generating ability, thereby requiring more fuel which adds to the cost of operation of the aircraft.